This invention relates generally to diazo dyes. More specifically the invention relates to a class of diazo dyes having a very high absorption for ultraviolet radiation, and a relatively low absorption for visible light. In other aspects, the invention relates to imaging methods utilizing these dyes.
Photolithographic and/or photoetch techniques are widely used in the fabrication of printed circuit boards, semiconductor devices, the preparation of printing plates, graphic arts, and a number of other such processes. Such photo techniques generally employ one or more masks, also referred to as phototools, which are often fabricated from a diazo based material.
Diazo dyes are based on the coupling reactions of various diazo compounds. These compounds, generally comprising a diazonium salt of an aromatic based nucleus, can undergo a chemical reaction with another molecular species, typically an aromatic compound referred to as a coupler, so as to form an azo dye compound. Such dyes typically have very high absorption coefficients, and by the appropriate choice of diazonium salt and coupler, various absorption spectra may be achieved. A variety of photographic systems which employ this basic reaction have been implemented. In some instances, light is used to initiate the coupling reaction, either by directly activating the reactants, or by unmasking a component of the system which undergoes further reaction. In other instances, light is employed to inactivate dye formation by inactivating one of the components of the system.
Diazo based dye systems have particular advantages in photolithography. The diazo system produces very high resolution allowing for preparation of finely detailed work. In addition, by appropriate choice of the imaging components, the absorption spectrum of the resultant azo dye can be optimized for particular applications. In accord with the present invention, there are provided diazo dye compounds which have very high optical absorptions in the near ultraviolet and violet portions of the spectrum, but have relatively low optical densities at longer wavelengths. A phototool or mask prepared from such materials has particular advantage in a number of techniques, since the low absorption at visible wavelengths allows for the ready positioning and alignment of a phototool with underlying structures, while the high optical density in the short wavelength regions is particularly well suited for absorbing the short wavelength illumination generally utilized in a number of photo techniques.
Dyes of the present invention may be employed in a number of applications. For example, the components of the dye, namely the diazonium salt and the coupler, may be incorporated into diazo imaging systems in which light either initiates a coupling reaction to form a negative imaging system, or inactivates a coupling reaction to form a direct positive imaging system. In other aspects of the present invention, the diazo dyes of the present invention may be directly synthesized, and subsequently applied to a substrate in an imagewise pattern, by printing or the like to form a photo mask. In other instances, an ink jet printer may be modified to use one or more components of the dye system of the present invention in order to generate a photo mask, and such a system may be placed under control of a computer for automated mask generation. These and other advantages and applications of the present invention will be apparent from the drawings, discussion and description which follow.
There is disclosed herein a novel class of diazo dye compounds which are formed by the coupling reaction of a diazonium salt selected from the group consisting of: 
wherein R equals hydrogen or an alkyl group, which is most preferably methyl, ethyl or propyl; Y is a halogen, preferably chlorine or fluorine; and X may be any anion, and most typically comprises a halogen, NO3xe2x88x92, HSO4xe2x88x92, BF4xe2x88x92, PF6xe2x88x92, and the like.
Most preferably, the diazonium salts are coupled with aromatic molecules selected from the group consisting of: 
Most preferably, R is hydrogen or alkyl; n is 0 or a whole number, and is most preferably 1, 2 or 3.
The present invention is also directed to a method of making a photo mask comprising disposing an imagewise pattern of the foregoing diazo dye onto a substrate. The imagewise pattern may be formed by various printing techniques such as impact printing, ink jet printing, screen printing and the like.
In one specific embodiment, an ink jet imaging process, preferably under computer control, is utilized to generate an imagewise pattern of the dyes of the present invention. In this embodiment, a first imaging component is disposed in the cartridge of a jet printer, and a second component is disposed in a substrate which is addressed, in an imagewise manner, by the jet printer. The first and second components are selected so that they react to produce the diazo dyes of the present invention. In one particular embodiment, the first component comprises a base such as ammonium hydroxide, and the second component comprises the diazonium salt and coupler of the present invention, together with an acid which prevents their reaction. Neutralization of the acid by the base allows dye formation. In another embodiment, a diazonium salt is disposed in the cartridge of the ink jet printer, and the coupler is disposed in the substrate. In yet other embodiments, the coupler is disposed in the printer cartridge, and the diazonium salt is in the substrate.